1. Field of the Invention
The present invention relates to a vehicle frame structure, and particularly to a vehicle frame structure for motorcycles.
2. Description of the Background Art
As conventionally provided in motorcycles, the vehicle main frame structure comprises a front half of the frame joined to a head pipe for supporting the front wheel to allow steering, and a rear half of the frame joined to a center frame for supporting the rear wheel via the swing arm. A main frame structure of this type is disclosed in JP-A No. 272569/2000. As disclosed in this document, the front half and rear half of the frame are made up of separate materials and provide a well-balanced, high-strength main frame while limiting the weight of the main frame.
Although the rear half of the main frame structure described in JP-A No. 272569/2000 is designed for comparatively low strength, in order to reduce weight, absorb shocks and achieve flexibility, the front half of the main frame is usually designed for comparatively high strength. The front half of the main frame requires high strength in order to boost bending and flexibility strength against input from the steering system. Main frames with a good balance of strength are in increasingly high demand to keep pace with high performance vehicles appearing in recent years. Along with this demand, greater strength is also desired in the portion of the frame joining the main frame and head pipe.
In view of this desideratum, the present invention provides a vehicle frame structure with a good balance of high strength in the main frame, as well as high strength in the portion of the frame joining the main frame and head pipe.